Abstract: Impurities in diesel oil may result in mechanical surface wear on the oil supply system of a diesel engine. As a precision plunger displacement pump with a ram clearance less than 0.0025 mm, the oil pump may suffer from wear in ram clearance if any fine impurity flows in, consequently, the engine may fail to operate normally. Therefore, some purifying measures shall be taken, ①settle the fuel oil in a tank for at least 72 hours befor filling it into fuel tank; ②filter the clarified fuel with clean cloth; ③prevent foreign materials from flowing into fuel tank; ④after filling, cover the fueling gun with dust protective cover.